Since you will NOT be installing DOS to the entire hard disk, but to just a small portion of it, you will need to be careful to not let the automatic setup program for DOS configure your hard drive partition for you, as it will want to fill the drive with DOS and you'll not have any room left for Linux.
When you first boot into the DOS setup program you will want to hit F3 twice to exit the setup and get to the A: prompt.
When pondering how much space to leave for DOS, remember that a very pared down Slackware Linux will require about 700meg (500meg for the root partition, 100meg for a swap partition, and 100meg for a /jnos partition).
From the A prompt you will want to use FDISK to access the hard disk and first view the present partitions on the drive. Do NOT just delete all the partitions on the drive first-- as that can be counterproductive depending on what's on that drive.
When you are viewing the partition table, if the whole drive is just one giant DOS partition then yes, you should delete that whole partition.
On the other hand, many Compaq owners, some Dell and IBM owners (and other manufacturers) will have what are called 'maintenance' partitions on the drive. These 'maintenance' partitions are NON-DOS partitions and usually relatively small. You will want to keep any of these small NON-DOS partitions so that your machine BIOS configuration and maintenance functionality can be maintained.If your machine is already setup with a small DOS partition and a larger secondary partition you might want to leave the smaller DOS partition in place and delete the secondary partition-- this will save you from having to install DOS (though, installing DOS is not a big deal).
Jnos for DOS does not require much room, 100meg should do most hamgates quite well.
I made a 500meg DOS partition (of the 5gig hard drive) in the machine used in writing these pages. 500meg is plenty more than the DOS Jnos would ever need and perhaps a bit of overkill.
Please also be aware that the DOS partition will also be available for use while you are running Linux, so the space set aside for DOS is not lost when you are not running DOS.
After you are done with the DOS Fdisk partition table tool you can reboot into the DOS installation floppy and let it do it's automatic install of DOS, as it would now just be putting DOS into that smaller partition on your hard drive.
I'll get into installing Jnos on DOS after I complete the pages on installing Jnos on Linux-- so you will have to wade through all the Linux work first.
Yea-- I'm mean and heartless. Waaaaa!